Pyrolysis Products of Packaging Waste Plastics

Waste plastics composition varies with collection area, sorting methods and time period, moreover several waste constituent polymer types occur in various waste categories. Nevertheless each customary plastic material will be discussed only in one of the three waste group included in this chapter. 

The majority of packaging plastic materials consists of polyolefins and vinyl polymers, namely polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). Obviously, these polymers have many other applications not only as packaging materials. Chemically they are all composed of saturated hydrocarbon chains of macro-molecular size their typical thermal decomposition pathway is free radical one initiated by the homolytic scission of a backbone carbon-carbon bond. In spite of the basic similarity of the initial cleavage, the decomposition of the hydrocarbon macroradicals is strongly influenced by fhe nafure of the side groups of the main chain. 

Division of the side groups from the main chain occurs only in those vinyl polymers in which the bonding of the substituent to the chain is weaker than the backbone C-C bond. The radical of the cleaved substituent draws hydrogen from the neighbouring carbon atom and is eliminated, for example as acetic acid from poly(vinyl acetate), or as hydrogen chloride from PVC. 

Plasticizer is added to PVC in many applications. Most frequently di(2-ethylhexyl phthalate) is used, boiling at 230°C, thus it may be evaporated from the molten PVC at 

Among polyesters synthesized from 1,4-benzenedicarboxylic acid and aliphatic diols, poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT) are the most frequently applied ones. Hydrolysis is evidently the easiest chemical recycling technique of polyesters, however they may be mixed with other waste plastics, thus it is useful to know the properties of their pyrolysis product. 

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